The present invention relates to a thread for forming a stent for vessels, implanted within vessels of a living body, such as lymph vessels, bile ducts or ureter, for maintaining a patency state of the lumen of the vessels, and to a stent for vessels employing the thread.
In angioplasty, mechanical techniques, such as balloon dilation technique or stent implanting technique, tend to injure blood vessels. In a site of lesion of the blood vessels, acute coronary occlusion, caused by thrombosis, or re-stenosis, caused by intimal hyperplasia of the blood vessel, as a curative reaction of the wall of the blood vessel, occurs frequently.
In acute coronary occlusion, thrombosis plays some role. For possible prevention, antithrombotic therapy by systemic administration of drugs via veins is customarily used.
On the other hand, re-stenosis is induced by excess hyperplasia of cells. Currently, researches into drugs for suppressing hyperplasia of cells are going on briskly, and several drugs have been found as giving acceptable results.
For deriving favorable results of these pharmaceuticals, it is necessary to administer the drugs at/in a high concentration or in a large quantity. It has, however, been indicated that side effects tend to be produced by such administration.
Recently, a local drug delivery system (LDDS) has come to be used as a safe and efficacious method for possible prevention of acute coronary occlusion or re-stenosis. In this LDDS, a stent is stirring up notice as a member for transporting the drug to a target site of the blood vessel. With the LDDS, employing the stent, local administration of the drug becomes possible by implanting the stent, carrying the drug, in a target site in the blood vessel. The stent can be implanted in a target site in the blood vessel, without obstructing the blood flow, for a prolonged time, and hence can be used as the LDDS which may produce a sufficient pharmaceutical effect for a prolonged period of time.
Meanwhile, the majority of the stents for blood vessels, used at present for clinical purposes, are made of metal. With metal, the drug cannot be mixed into the material, such that the drug can be applied only to its surface. Among a variety of methods for depositing the drug to the metal stent, there are a coating method and a bonding method, as disclosed in the Japanese Laid-Open Patent Publication H-8-33718. When the drug is deposited on the surface of the metal stent by the coating method or the bonding method, there is raised a problem that the drug itself may peel off from the stent surface. Furthermore, it is difficult to deposit an amount of the drug sufficient to derive the pharmaceutical effect. In addition, since the metal stent, implanted in the blood vessel, remains permanently as a foreign substance, there is a possibility that re-stenosis may be produced in the stent implant site of the blood vessel.
With the LDDS, it is necessary to control the content of the drug, the amount of drug release per unit time and the time period of drug release. In order to take precautions against acute coronary occlusion or re-stenosis by the LDDS more effectively, such control is desirable in which the effective concentration of the drug in the target blood vessel site may be maintained and in which the drug may be released for a predetermined period to the blood vessel wall and into the blood.